Crystallized glass of three-dimensional shape, chemically strengthened glass of three-dimensional shape, and method for producing crystallized glass of three-dimensional shape and chemically strengthened glass of three-dimensional shape

ABSTRACT

The present invention provides crystallized glass of three-dimensional shape for easily producing chemically strengthened glass of three-dimensional shape that resists damage and has exceptional transparency. This crystallized glass of three-dimensional shape: contains crystals; has light transmittance in terms of a thickness of 0.8 mm of 80% or higher; and contains 45-74% SiO2, 1-30% Al2O3, 1-25% Li2O, 0-10% Na2O, 0-5% K2O, a total of 0-15% of SnO2 and/or ZrO2, and 0-12% P2O5, these amounts expressing the oxide-based mass percentage.

TECHNICAL FIELD

The present invention relates to a three-dimensionally shapedcrystallized glass having high transparency and excellent chemicalstrengthening properties, and relates to a production method thereof.The present invention also relates to a three-dimensionally shapedchemically strengthened glass and a production method thereof.

BACKGROUND ART

A thin chemically strengthened glass having high-strength is used as acover glass of a display unit of a mobile device such as cell phone andsmartphone or as a cover glass of an in-vehicle display member such asinstrument panel and head-up display (HUD). In such a display unit, acover glass having a three-dimensional shape (curved shape) is sometimesrequired so as to improve the operability and visibility. Thethree-dimensionally shaped cover glass is produced by a method in whicha flat glass sheet is heated and then subjected to bend-forming(sometimes referred to as three-dimensional forming) using forming molds(see, Patent Literature 1).

Patent Literature 2 discloses a lithium aluminosilicate glass capable ofbeing three-dimensionally formed and chemically strengthened.

Patent Literature 3 discloses a chemically strengthened crystallizedglass.

CITATION LIST Patent Literature

Patent Literature 1: International Publication WO2014/167894

Patent Literature 2: JP-T-2013-520385 (the term “JP-T” as used hereinmeans a published Japanese translation of a PCT patent application)

Patent Literature 3: JP-T-2016-529201

SUMMARY OF INVENTION Technical Problem

The chemical strengthening properties of a crystallized glass aregreatly affected by a glass composition and a precipitated crystal.Scratch resistance and transparency of the crystallized glass are alsogreatly affected by a glass composition and a precipitated crystal. Inorder to obtain a crystallized glass excellent in both chemicalstrengthening properties and transparency, the glass composition andprecipitated crystal need to be subtly adjusted.

The method for obtaining a three-dimensionally shaped crystallized glassincludes a method in which an amorphous glass is bend-formed and thencrystallized, a method in which an amorphous glass is crystallized andthen processed into a three-dimensional shape by grinding or othermethods, and a method in which an amorphous glass is crystallized andthen bend-formed.

According to the method in which an amorphous glass is bend-formed andthen crystallized, since a heat treatment is performed after theforming, not only deformation is likely to occur but also a dimensionalchange is caused at the time of crystallization of the amorphous glass,thereby making it difficult to obtain a desired shape. According to themethod in which an amorphous glass is crystallized and then processedinto a three-dimensional shape by grinding or other methods, thegrinding processing takes a long time and therefore the productionefficiency is low.

Then, it is preferable to crystallize an amorphous glass and thenperform bend-forming. However a crystallized glass generally has ahigher softening temperature, compared with an amorphous glass, and thusbend-forming thereof is difficult. In addition, when a transparentcrystallized glass is heated at a high temperature so as to bend-formthe glass, crystals in the crystallized glass are likely to growexcessively, thereby giving rise to a problem such as reduction intransparency.

In consideration of these, an object of the present invention is toprovide a three-dimensionally shaped crystallized glass for easilyproducing a three-dimensionally shaped chemically strengthened glassthat is scratch-resistant and has excellent transparency.

In addition, an object of the present invention is to provide athree-dimensionally shaped chemically strengthened glass that isscratch-resistant and has excellent transparency, obtained by chemicallystrengthening the three-dimensionally shaped crystallized glass above.

Furthermore, an object of the present invention is to provide aproduction method of a chemically strengthened glass that is thethree-dimensionally shaped crystallized glass above.

Solution to Problem

The present invention provides a three-dimensionally shaped crystallizedglass including a crystal, the glass having a light transmittance of 80%or more in terms of a thickness of 0.8 mm and including, in mass % on anoxide basis, from 45 to 74% of SiO₂, from 1 to 30% of Al₂O₃, from 1 to25% of Li₂O, from 0 to 10% of Na₂O, from 0 to 5% of K₂O, from 0 to 15%in total of either one or more of SnO₂ and ZrO₂, and from 0 to 12% ofP₂O₅.

In addition, the present invention provides a three-dimensionally shapedchemically strengthened glass having a compressive stress layer on asurface thereof, the glass being a crystallized glass including acrystal, having a light transmittance of 80% or more in terms of athickness of 0.8 mm and including, in mass % on an oxide basis, from 45to 74% of SiO₂, from 1 to 30% of Al₂O₃, from 1 to 25% of Li₂O, from 0 to10% of Na₂O, from 0 to 5% of K₂O, from 0 to 15% in total of either oneor more of SnO₂ and ZrO₂, and from 0 to 12% of P₂O₅.

The present invention also provides a production method of a glass forchemical strengthening, the method including heating and crystallizing aglass including, in mass % on an oxide basis, from 45 to 74% of SiO₂,from 1 to 30% of Al₂O₃, from 2 to 25% of Li₂O, from 0 to 10% of Na₂O,from 0 to 5% of K₂O, from 0 to 15% in total of either one or more ofSnO₂ and ZrO₂, and from 0 to 12% of P₂O₅, and bend-forming a resultingcrystallized glass under heating.

Furthermore, the present invention provides a production method of achemically strengthened glass, including heating and crystallizing aglass including, in mass % on an oxide basis, from 45 to 74% of SiO₂,from 1 to 30% of Al₂O₃, from 2 to 25% of Li₂O, from 0 to 10% of Na₂O,from 0 to 5% of K₂O, from 0 to 15% in total of either one or more ofSnO₂ and ZrO₂, and from 0 to 12% of P₂O₅, bend-forming a resultingcrystallized glass under heating, and thereafter, chemicallystrengthening the glass.

Advantageous Effects of Invention

In the present invention, a three-dimensionally shaped crystallizedglass for easily producing a three-dimensionally shaped chemicallystrengthened glass that is scratch-resistant and has excellenttransparency, is obtained.

In addition, the chemically strengthened glass of the present inventionis scratch-resistant, has excellent transparency, and can be easilyproduced by chemically strengthening the three-dimensionally shapedcrystallized glass of the present invention.

Furthermore, in the production method of the chemically strengthenedglass of the present invention, the three-dimensionally shapedcrystallized glass of the present invention is obtained.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective diagram illustrating one example of the shape ofthe three-dimensionally shaped glass of the present invention.

FIG. 2 is a perspective diagram illustrating one example of the shape ofthe three-dimensionally shaped glass of the present invention.

FIG. 3 is a perspective diagram illustrating one example of the shape ofthe three-dimensionally shaped glass of the present invention.

FIG. 4 is a diagram illustrating one example of the X-ray diffractionpattern of the crystallized glass.

FIG. 5 is a diagram illustrating one example of the X-ray diffractionpattern of the crystallized glass.

FIG. 6 is a schematic diagram illustrating a test method of bendformability for the crystallized glass; (a) of FIG. 6 illustrates thestate before bending; and (b) of FIG. 6 illustrates the state of beingheated and thus bent.

DESCRIPTION OF EMBODIMENTS

The embodiments of the present invention are described below. However,the present invention is not limited to the embodiments described below.In the following drawings, members and regions having the same actionsmay be described by assigning the same symbols thereto, and duplicateddescriptions thereof may be omitted or simplified. In addition, theembodiments in the drawings are schematically illustrated for clearlydescribing the present invention and not always show the actual size orscale exactly.

In the present description, the numerical range expressed using “to” isused in the meaning of including numerical values described before andafter it as the lower limit value and the upper limit value.

In the present description, the “amorphous glass” and the “crystallizedglass” are collectively referred to as “glass”.

In the present description, the “amorphous glass” means a glass in whicha diffraction peak indicating a crystal cannot be observed by a powderX-ray diffraction method.

In the present description, the “crystallized glass” is a glass obtainedby heating the “amorphous glass” to precipitate a crystal therein andmeans a glass containing a crystal.

In powder X-ray diffractometry, a region where 2θ is from 10° to 80° ismeasured using CuKα radiation, and when a diffraction peak appears, aprecipitated crystal is identified by, for example, a Hanawalt method.

In the present description, the “chemically strengthened glass” means aglass having been subjected to a chemical strengthening treatment, andthe “glass for chemical strengthening” means a glass before beingsubjected to a chemical strengthening treatment.

Furthermore, in the present description, the “base composition of achemically strengthened glass” means a glass composition of a glass forchemical strengthening. Unless an immoderate ion exchange treatment isperformed, a glass composition of a part deeper than a depth of acompressive stress layer (DOL) in a chemically strengthened glass is thesame as the base composition of the chemically strengthened glass.

In the present description, unless otherwise indicated, the glasscomposition is expressed in mass % on an oxide basis, and mass % issimply written as “%”.

In the present description, the “substantially free of” means that thecontent is not higher than a level of impurities contained in rawmaterials or the like, i.e., the substance is not intentionally added.In the present description, when the “substantially free of a certaincomponent” is stated, the content of the component is specifically, forexample, less than 0.1%.

In the present description, the “stress profile” means a profile showinga compressive stress value by using a depth from a glass surface as thevariable. In the stress profile, the tensile stress is expressed as anegative compressive stress.

The “compressive stress value (CS)” can be measured by thinning a crosssection of a glass and analyzing the thinned sample with a birefringenceimaging system. The birefringence imaging system includes, for example,a birefringence imaging system Abrio-IM manufactured by TokyoInstruments, Inc. The value can also be measured by use ofscattered-light photoelasticity. In this method, the CS can be measuredby making light incident from a surface of a glass and analyzingpolarization of the scattered light. The stress meter usingscattered-light photoelasticity includes, for example, a scattered-lightphotoelastic stress meter SLP-1000 manufactured by Orihara ManufacturingCo., Ltd.

The “depth of compressive stress layer (DOL)” is a depth at which thecompressive stress value (CS) is zero.

In the following, the surface compressive stress at a depth of DOL/4 issometimes denoted by CS₁, and the compressive stress at a depth of DOL/2is sometimes denoted by CS₂.

In addition, the depth at which the compressive stress value becomesCS/2 is denoted by DOL₁, and m₁ represented by the following expressionis taken as an inclination of the stress profile from the glass surfaceto the depth DOL₁.

m ₁=(CS−CS/2)/(0−DOL ₁)

m₂ represented by the following expression is taken as an inclination ofthe stress profile from the depth DOL/4 to the depth DOL/2.

m ₂=(CS ₁ −CS ₂)/(DOL/4−DOL/2)

m₃ represented by the following expression is taken as an inclination ofthe stress profile from the depth DOL/2 to the depth DOL.

m ₃=(CS ₂−0)/(DOL/2−DOL)

In the present description, the “internal tensile stress (CT)” means atensile stress value at a depth corresponding to ½ of a sheet thicknesst.

In the present description, the “light transmittance” means an averagetransmittance of light at a wavelength of 380 nm to 780 nm.

In the present description, the “haze value” means a haze value measuredwith a C illuminant according to JIS K3761:2000.

In the present description, the “Vickers hardness” is a Vickers hardness(HV0.1) specified in JIS R1610:2003.

In addition, the “fracture toughness value” means anindentation-fracture method (IF method) fracture toughness valuespecified in JIS R1607:2010.

In the present description, the “three-dimensional shape” means a shapeobtained by bending a flat sheet. Incidentally, the three-dimensionalshape is not limited to a shape having a uniform thickness as a wholebut may be a shape having portions differing in the thickness.

<Three-Dimensionally Shaped Crystallized Glass>

FIG. 1 is a perspective diagram illustrating one example of thethree-dimensionally shaped crystallized glass of the present embodiment(hereinafter, sometimes referred to as “the present three-dimensionallyshaped glass”). In FIG. 1, a concave shape is depicted, but the presentthree-dimensionally shaped glass may have a convex shape. In FIG. 1, aglass having a flat sheet shape in the central part is illustrated, butthe present three-dimensionally shaped glass may be curved as a whole.In addition, the present three-dimensionally shaped glass may have athree-dimensional shape composed of a plurality of R shapes asillustrated in FIG. 2 and FIG. 3.

The present three-dimensionally shaped glass has high transparency andtherefore, is suitable for a cover glass, etc. in the display part of amobile terminal, etc. The light transmittance in terms of a thickness of0.8 mm of the present three-dimensionally shaped glass is preferably 80%or more, because the screen is viewed easily when used for a cover glassof a mobile display, and is more preferably 85% or more, still morepreferably 86% or more, particularly preferably 88% or more. The lighttransmittance of the present three-dimensionally shaped glass in termsof a thickness of 0.8 mm is preferably higher, but it is usually 91% orless, or 90% or less. The light transmittance of 90% is comparable tothat of a general amorphous glass.

The haze value of the present three-dimensionally shaped glass in termsof a thickness of 0.8 mm is preferably 1.5% or less, more preferably1.2% or less, still more preferably 1% or less, yet still morepreferably 0.8% or less, and most preferably 0.5% or less. On the otherhand, in the case where the haze can hardly be reduced unless thecrystallinity is reduced, in order to, e.g., increase the mechanicalstrength, the haze value of the present three-dimensionally shaped glassin terms of a thickness of 0.8 mm is preferably 0.05% or more, morepreferably 0.1% or more.

The present three-dimensionally shaped glass is a crystallized glass andtherefore, the strength is high compared with an amorphous glass. Inaddition, the Vickers hardness is large, and the glass isscratch-resistant.

In order to enhance the abrasion resistance, the Vickers hardness of thepresent three-dimensionally shaped glass is preferably 680 or more, morepreferably 700 or more, and still more preferably 740 or more, yet stillmore preferably 780 or more, particularly preferably 800 or more.

However, if the Vickers hardness is too large, the processing may becomedifficult. Therefore, the Vickers hardness of the presentthree-dimensionally shaped glass is preferably 1,100 or less, morepreferably 1,050 or less, still more preferably 1,000 or less.

The crystallized glass (hereinafter, sometimes referred to as “thepresent crystallized glass”) constituting the presentthree-dimensionally shaped glass contains crystals, and it is preferableto contain a lithium aluminosilicate crystal or a lithium silicatecrystal. In the case of containing a lithium aluminosilicate crystal ora lithium silicate crystal, these crystals are also ion-exchanged duringa chemical strengthening treatment and therefore, high strength isobtained. Examples of the lithium aluminosilicate crystal include aβ-spodumene crystal and a petalite crystal. Examples of the lithiumsilicate crystal include a lithium metasilicate crystal and a lithiumdisilicate crystal.

In the case of increasing the strength after chemical strengthening, itis preferable for the present crystallized glass to contain aβ-spodumene crystal. In the case of improving the transparency andformability while keeping the chemical strengthening properties, it ispreferable for the present crystallized glass to contain a lithiummetasilicate crystal.

The β-spodumene crystal is represented by LiAlSi₂O₆ and is a crystalshowing diffraction peaks at Bragg angles (2θ) of 25.55°±0.05°,22.71°±0.05°, and 28.20°±0.05° in an X-ray diffraction spectrum.

FIG. 2 illustrates examples of X-ray diffraction patterns of acrystallized glass (a glass for chemical strengthening) containing aβ-spodumene crystal and a crystallized glass (chemically strengthenedglass) obtained by chemically strengthening the crystallized glassabove. In FIG. 2, the solid line is an X-ray diffraction patternmeasured for the crystallized glass sheet before strengthening, and adiffraction line of the β-spodumene crystal indicated by black circlesis observed in FIG. 2. The broken line shows an X-ray diffractionpattern measured for the crystallized glass (chemically strengthenedglass) sheet after chemical strengthening. It is considered that thepositions of diffraction peaks are shifted to the lower angle side bychemical strengthening because the lattice spacing is increased due tooccurrence of ion exchange between small ions in the crystal and largeions in the molten salt.

However, when the present inventors compared powder X-ray diffractionpatterns before and after chemical strengthening, such a shift of adiffraction line was not observed. The reason therefor is consideredbecause a change in the lattice spacing due to a chemical strengtheningtreatment occurs only in the vicinity of the surface of the glass sheetand no change is caused in the internal crystals by a chemicalstrengthening treatment.

In the crystallized glass containing a β-spodumene crystal, the surfacecompressive stress (CS) tends to be increased by chemical strengthening,compared with a crystallized glass containing other crystals. This maybe because the crystal structure of the β-spodumene crystal is dense andtherefore, when ions in the precipitated crystal are substituted bylarger ion through an ion exchange treatment for chemical strengthening,the compressive stress generated along with a change in the crystalstructure increases.

The β-spodumene crystal is known to have a high crystal growth rate.Therefore, in the crystallized glass containing a β-spodumene crystal,the crystals contained therein easily growth and consequently, in manycases, such a glass has low transparency and large haze value. However,since the present three-dimensionally shaped glass contains a largenumber of microcrystals, the transparency is high and the haze value issmall.

The lithium metasilicate crystal is represented by Li₂SiO₃ and is acrystal showing diffraction peaks at Bragg angles (2θ) of 26.98±0.2,18.88±0.2, and 33.05±0.2 in an X-ray diffraction spectrum. FIG. 3illustrates an example of the X-ray diffraction pattern of acrystallized glass containing a lithium metasilicate crystal.

The crystallized glass containing a lithium metasilicate crystal has ahigh fracture toughness value compared with an amorphous glass, andintense fracture is difficult to occur even when a large compressivestress is formed by chemical strengthening. An amorphous glass capableof precipitating a lithium metasilicate crystal may precipitate alithium disilicate crystal depending on the heat treatment conditions,etc., and when a lithium metasilicate crystal and a lithium disilicatecrystal are contained at the same time, the transparency is reduced.Then, in terms of enhancing the transparency, it is preferred that thecrystallized glass containing lithium metasilicate does not containlithium disilicate. The phrase “does not contain lithium disilicate” asused herein means that in the above-described X-ray diffractometry, adiffraction peak of a lithium disilicate crystal is not observed.

In the case of lowering the bend-forming temperature, the presentcrystallized glass preferably contains a petalite crystal or a lithiummetasilicate crystal. A crystallized glass containing such a crystal hasa low crystallization treatment temperature and a low softeningtemperature and therefore, the forming temperature tends to be easilylowered.

For increasing the mechanical strength, the crystallinity of the presentcrystallized glass is preferably 10% or more, more preferably 15% ormore, still more preferably 20% or more, particularly preferably 25% ormore. On the other hand, for enhancing the transparency, thecrystallinity of the present crystallized glass is preferably 70% orless, more preferably 60% or less, particularly preferably 50% or less.A low crystallinity is preferable also in terms of that bend-forming orthe like is easily performed by heating.

The crystallinity can be calculated from X-ray diffraction intensity bya Rietveld method. The Rietveld method is described in “Handbook ofCrystal Analysis” edited by the “Handbook of Crystal Analysis” EditingCommittee of the Crystallographic Society of Japan (published byKyoritsu Shuppan Co., Ltd., 1999, pp. 492-499).

The average particle size of precipitated crystals in the presentcrystallized glass is preferably 300 nm or less, more preferably 200 nmor less, still more preferably 150 nm or less, and particularlypreferably 100 nm or less. The average particle size of precipitatedcrystals can be calculated from powder X-ray diffraction intensity bythe Rietveld method.

The crystallized glass containing a β-spodumene crystal is also known tohave a small thermal expansion coefficient. In the case where thepresent crystallized glass contains β-spodumene, the average thermalexpansion coefficient thereof at 50° C. to 350° C. is preferably30×10⁻⁷/° C. or less, more preferably 25×10⁻⁷/° C. or less, still morepreferably 20×10⁻⁷/° C. or less, and particularly preferably 15×10⁻⁷/°C. or less. The average thermal expansion coefficient at 50° C. to 350°C. is usually 10×10⁻⁷/° C. or more.

On the other hand, in the case where the present crystallized glasscontains a lithium metasilicate crystal, the average thermal expansioncoefficient thereof at 50° C. to 350° C. is preferably 10×10⁻⁷/° C. ormore, more preferably 11×10⁻⁷/° C. or more, still more preferably12×10⁻⁷/° C. or more, and particularly preferably 13×10⁻⁷/° C. or more.If the thermal expansion coefficient is too large, cracking is likely tooccur during heat treatment. Accordingly, in the case where the presentcrystallized glass contains a lithium metasilicate crystal, the averagethermal expansion coefficient thereof at 50° C. to 350° C. is preferably160×10⁻⁷/° C. or less, more preferably 150×10⁻⁷/° C. or less, stillpreferably 140×10⁻⁷/° C. or less.

The fracture toughness value of the present crystallized glass ispreferably 0.8 MPa·m^(1/2) or more, more preferably 1 MPa·m^(1/2) ormore. Within this range, fragments are less likely to scatter uponbreakage of the strengthened glass.

The Young's modulus of the present crystallized glass is preferably 80GPa or more, more preferably 86 GPa or more, still more preferably 90GPa or more, and particularly preferably 100 GPa or more. When theYoung's modulus is increased, fragments are less likely to scatter uponbreakage of the strengthened glass.

In the case where the present crystallized glass contains a lithiumaluminosilicate crystal, the glass preferably includes, in mass % on anoxide basis, from 58 to 74% of SiO₂, from 5 to 30% of Al₂O₃, from 1 to14% of Li₂O, from 0 to 5% of Na₂O, from 0 to 2% of K₂O, from 0.5 to 12%in total of either one or more of SnO₂ and ZrO₂, and from 0 to 6% ofP₂O₅.

In the composition above, it is more preferable to include from 2 to 14%of Li₂O, and it is also more preferred that the total (Na₂O+K₂O) of thecontents of Na₂O and K₂O is from 1 to 5%.

In addition, it is more preferred that the glass includes from 58 to 70%of SiO₂, from 15 to 30% of Al₂O₃, from 2 to 10% of Li₂O, from 0 to 5% ofNa₂O, from 0 to 2% of K₂O, from 0.5 to 6% of SnO₂, from 0.5 to 6% ofZrO₂, and from 0 to 6% of P₂O₅ and Na₂O+K₂O is from 1 to 5%.

In other words, the present three-dimensionally shaped glass ispreferably a glass obtained by crystallizing an amorphous glass havingthe composition above.

In the case where the present crystallized glass contains a lithiumsilicate crystal, the glass preferably includes, in mass % on an oxidebasis, from 45 to 75% of SiO₂, from 1 to 20% of Al₂O₃, from 10 to 25% ofLi₂O, from 0 to 12% of P₂O₅, from 0 to 15% of ZrO₂, from 0 to 10% ofNa₂O, and from 0 to 5% of K₂O.

<Chemically Strengthened Glass>

The present three-dimensionally shaped glass is preferably chemicallystrengthened. The three-dimensionally shaped chemically strengthenedglass of this embodiment (hereinafter, sometimes referred to as “thepresent strengthened glass”) obtained by chemically strengthening thepresent three-dimensionally shaped glass is described.

The surface compressive stress (CS) of the present strengthened glass ispreferably 600 MPa or more, because cracking is hardly caused bydeformation such as deflection. The surface compressive stress of thepresent strengthened glass is more preferably 800 MPa or more.

The depth of compressive stress layer (DOL) of the present strengthenedglass is preferably 80 μm or more, because cracking hardly occurs evenwhen the surface is flawed. The DOL of the present strengthened glass ispreferably 100 μm or more.

In addition, the maximum depth (hereinafter, sometimes referred to as“50 MPa depth”) at which the compressive stress value is 50 MPa or moreis preferably 80 μm or more, because cracking hardly occurs even whenthe glass is dropped on a hard surface such as asphalt. The 50 MPa depthis more preferably 90 μm or more, and particularly preferably 100 μm ormore.

In the present strengthened glass, the inclination m₁ of the stressprofile from the glass surface to the depth DOL₁ is preferably −50MPa/μm or less, more preferably −55 MPa/μm or less, and still morepreferably −60 MPa/μm or less. The chemically strengthened glass is aglass having a compressive stress layer formed in the surface. Since atensile stress is generated in a portion far from the surface, thestress profile thereof has a negative inclination from the surface at adepth of zero toward the inside. Accordingly, m₁ is a negative value,and when an absolute value thereof is large, a stress profile having alarge surface compressive stress CS and a small internal tensile stressCT is obtained.

The inclination m₂ of the stress profile from a depth of DOL/4 to adepth of DOL/2 has a negative value. In order to suppress scattering offragments upon breakage of the strengthened glass, the inclination m₂ ispreferably −5 MPa/μm or more, more preferably −3 MPa/μm or more, andstill more preferably −2 MPa/μm or more. If m₂ is too large, the 50 MPadepth is reduced, and there is a concern that the drop strength toasphalt may lack. In order to increase the 50 MPa depth, m₂ ispreferably −0.3 MPa/μm or less, more preferably −0.5 MPa/μm or less, andstill more preferably −0.7 MPa/μm or less.

In the present strengthened glass, the inclination m₃ of the stressprofile from a depth of DOL/2 to DOL has a negative value. In order tosuppress scattering of fragments upon breakage of the strengthenedglass, m₃ is preferably −5 MPa/mm or more, more preferably −4 MPa/μm ormore, still more preferably −3.5 MPa/μm or more, and particularlypreferably −2 MPa/μm or more. If the absolute value of m₃ is too small,the 50 MPa depth is reduced, and cracking is likely to occur when theglass is flawed. In order to increase the 50 MPa depth, m₃ is preferably−0.3 MPa/μm or less, more preferably −0.5 MPa/μm or less, and still morepreferably −0.7 MPa/μm or less.

The ratio m₂/m₃ of the inclination m₂ to the inclination m₃ ispreferably 2 or less, because deep DOL and small CT are obtained. Theratio m₂/m₃ is more preferably 1.5 or less, and still more preferably 1or less. In order to prevent occurrence of cracks in an end face of thestrengthened glass, the ratio m₂/m₃ is preferably 0.3 or more, morepreferably 0.5 or more, and still more preferably 0.7 or more.

The internal tensile stress (CT) of the present strengthened glass ispreferably 110 MPa or less, because fragments are less likely to scatterupon breakage of the strengthened glass. The CT is more preferably 100MPa or less, still more preferably 90 MPa or less. On the other hand,when the CT is reduced, the CS is also reduced, resulting in a tendencythat sufficient strength is difficult to be obtained. Therefore, the CTis preferably 50 MPa or more, more preferably 55 MPa or more, and stillmore preferably 60 MPa or more.

The four point bending strength of the present strengthened glass ispreferably 900 MPa or more.

Here, the four point bending strength is measured using a test piece of40 mm×5 mm×0.8 mm under the conditions of a lower span of 30 mm, anupper span of 10 mm and a cross head speed of 0.5 mm/min. An averagevalue of 10 test pieces is taken as the four point bending strength.

The light transmittance and haze value of the present strengthened glassare substantially the same as those of the three-dimensionally shapedglass before chemical strengthening and therefore, descriptions thereofare omitted. In addition, as with the three-dimensionally shaped glassbefore chemical strengthening, it is preferable for the presentstrengthened glass to contain a β-spodumene crystal.

The Vickers hardness of the present strengthened glass tends to belarger than that of the three-dimensionally shaped glass beforestrengthening.

The Vickers hardness of the present strengthened glass is preferably 720or more, more preferably 740 or more, still more preferably 780 or more,and yet still more preferably 800 or more. On the other hand, theVickers hardness of the present strengthened glass is usually 950 orless.

<Glass Composition>

Here, the glass composition of the present crystallized glass isdescribed. The composition of the present crystallized glass is as awhole the same as the composition of the amorphous glass beforecrystallization treatment.

In addition, the present strengthened glass is obtained by chemicallystrengthening the present three-dimensionally shaped glass composed ofthe present crystallized glass and unless an immoderate ion exchangetreatment is performed, the composition of the present strengthenedglass is as a whole the same as the composition of the presentcrystallized glass described below.

The present crystallized glass includes, in mass % on an oxide basis,from 45 to 74% of SiO₂, from 1 to 30% of Al₂O₃, from 1 to 25% of Li₂O,from 0 to 10% of Na₂O, from 0 to 5% of K₂O, from 0 to 15% in total ofeither one or more of SnO₂ and ZrO₂, and from 0 to 12% of P₂O₅.

In the case where the present crystallized glass contains a lithiumaluminosilicate crystal, the glass preferably includes, in mass % on anoxide basis, from 58 to 74% of SiO₂, from 5 to 30% of Al₂O₃, from 1 to14% of Li₂O, from 0 to 5% of Na₂O, from 0 to 2% of K₂O, from 0.5 to 12%in total of either one or more of SnO₂ and ZrO₂, and from 0 to 6% ofP₂O₅.

In the composition above, it is more preferable to include from 2 to 14%of Li₂O, and it is also more preferred that the total (Na₂O+K₂O) of thecontents of Na₂O and K₂O is from 1 to 5%.

In addition, it is still more preferred that the glass includes, in mass% on an oxide basis, from 58 to 70% of SiO₂, from 15 to 30% of Al₂O₃,from 2 to 10% of Li₂O, from 0 to 5% of Na₂O, from 0 to 2% of K₂O, from0.5 to 6% of SnO₂, from 0.5 to 6% of ZrO₂, and from 0 to 6% of P₂O₅ andNa₂O+K₂O is from 1 to 5%.

In the case where the present crystallized glass contains a lithiumsilicate crystal, the glass preferably includes, in mass % on an oxidebasis, from 45 to 75% of SiO₂, from 1 to 20% of Al₂O₃, from 10 to 25% ofLi₂O, from 0 to 12% of P₂O₅, from 0 to 15% of ZrO₂, from 0 to 10% ofNa₂O, and from 0 to 5% of K₂O.

These preferable glass compositions are described below.

SiO₂ is a component forming a network structure of the glass. Inaddition, SiO₂ is a component enhancing the chemical durability, is aconstituent component of a lithium aluminosilicate crystal, and is alsoa constituent component of a lithium silicate crystal. The content ofSiO₂ is 45% or more, preferably 50% or more, and more preferably 55% ormore. In the case of increasing particularly the strength, the contentof SiO₂ is preferably 58% or more, more preferably 60% or more, andstill more preferably 64% or more. On the other hand, if the content ofSiO₂ is too large, the meltability decreases significantly. Therefore,the content of SiO₂ is 74% or less, preferably 70% or less, morepreferably 68% or less, and still more preferably 66% or less.

Al₂O₃ is a component effective in increasing the surface compressivestress generated by chemical strengthening, and is essential. Al₂O₃ is aconstituent component of a lithium aluminosilicate crystal. The contentof Al₂O₃ is 1% or more, preferably 2% or more, more preferably 5% ormore, and still more preferably 8% or more. In the case of precipitatinga β-spodumene crystal, the content of Al₂O₃ is more preferably 15% ormore, and still more preferably 20% or more. On the other hand, if thecontent of Al₂O₃ is too large, the devitrification temperature of theglass rises. The content of Al₂O₃ is 30% or less, and preferably 25% orless. In order to lower the forming temperature, the content of Al₂O₃ ismore preferably 20% or less, and still more preferably 15% or less.

Li₂O is a component forming a surface compressive stress by the effectof ion exchange, is a constituent component of a lithium aluminosilicatecrystal and a lithium silicate crystal, and is essential.

The content of Li₂O is 1% or more, preferably 2% or more, morepreferably 4% or more. For increasing the precipitated amount of lithiummetasilicate crystal, the content of Li₂O is more preferably 10% ormore, still more preferably 15% or more, and particularly preferably 20%or more. In the case of lithium metasilicate, the content of Li₂O ispreferably 25% or less, more preferably 22% or less, and still morepreferably 20% or less. On the other hand, for precipitating a lithiumaluminosilicate crystal, the content of Li₂O is preferably 14% or less,and in the case of precipitating a β-spodumene crystal, the content ispreferably 10% or less, more preferably 8% or less, and still morepreferably 6% or less.

In the case where the present crystallized glass contains a β-spodumenecrystal, the content ratio Li₂O/Al₂O₃ of Li₂O and Al₂O₃ is preferably0.3 or less, because the transparency is improved.

Na₂O is a component improving the meltability of the glass.

Although Na₂O is not essential, the content of Na₂O in the presentcrystallized glass is preferably 0.5% or more, and more preferably 1% ormore. If the content of Na₂O is too large, a lithium aluminosilicatecrystal or lithium silicate crystal becomes difficult to beprecipitated, or the chemical strengthening properties are deteriorated.Therefore, the content of Na₂O in the present crystallized glass ispreferably 15% or less, more preferably 12% or less, and still morepreferably 10% or less. For precipitating a β-spodumene crystal, thecontent of Na₂O is preferably 5% or less, more preferably 4% or less,and still more preferably 3% or less.

As with Na₂O, K₂O is a component lowering the melting temperature of theglass and may be contained. In the case where the present crystallizedglass contains K₂O, the content thereof is preferably 0.5% or more, andmore preferably 1% or more. For lowering the forming temperature, thecontent of K₂O is more preferably 1.5% or more, and still morepreferably 2% or more.

The total content Na₂O+K₂O of Na₂O and K₂O is preferably 1% or more, andmore preferably 2% or more.

If the content of K₂O is too large, the chemical strengtheningproperties are deteriorated. Therefore, in the case where the presentcrystallized glass contains K₂O, the content thereof is preferably 8% orless, more preferably 7% or less, still more preferably 6% or less, andparticularly preferably 5% or less. In order to facilitate theprecipitation of a lithium aluminosilicate crystal, the content of K₂Ois preferably 2% or less. In this case, if the total content Na₂O+K₂O ofNa₂O and K₂O is excessively large, there is a concern that thetransparency may be deteriorated. For enhancing the transparency, thetotal content is preferably 5% or less, more preferably 4% or less, andstill more preferably 3% or less.

In the crystallized glass containing lithium metasilicate, in order tosatisfy both the chemical strengthening properties and the precipitationof a lithium metasilicate crystal, the content of K₂O is preferably 4%or less, more preferably 3% or less, and particularly preferably 2% orless.

Both ZrO₂ and SnO₂ are not essential but are a component constituting acrystal nucleus at the time of crystallization treatment, and it ispreferable to contain either one or more of these. In order to produce acrystal nucleus, the total content SnO₂+ZrO₂ of SnO₂ and ZrO₂ ispreferably 0.5% or more, and more preferably 1% or more. In order toform a large number of crystal nuclei and thereby enhance thetransparency, the total content is preferably 3% or more, morepreferably 4% or more, still more preferably 5% or more, particularlypreferably 6% or more, and most preferably 7% or more. In order toprecipitate lithium metasilicate, it is preferable to contain ZrO₂. Inthis case, the content of ZrO₂ is preferably 1% or more, more preferably2% or more, still more preferably 4% or more, particularly preferably 6%or more, and most preferably 7% or more. Furthermore, in order tosuppress devitrification during glass melting, the SnO₂+ZrO₂ ispreferably 15% or less, and more preferably 14% or less. For making adefect due to unmelted material difficult to occur in the glass, thetotal content is preferably 12% or less, more preferably 10% or less,still more preferably 9% or less, and particularly preferably 8% orless.

In the case of precipitating a β-spodumene crystal, the content of SnO₂is preferably 0.5% or more, more preferably 1% or more, and still morepreferably 1.5% or more. The content of SnO₂ is preferably 6% or less,because a defect due to an unmelted material is difficult to occur inthe glass, and the content is more preferably 5% or less, still morepreferably 4% or less.

SnO₂ is also a component enhancing the solarization resistance. In orderto suppress solarization, the content of SnO₂ is preferably 1% or more,and more preferably 1.5% or more.

In the case of precipitating a β-spodumene crystal, the content of ZrO₂is preferably 0.5% or more, more preferably 1% or more. In this case, ifthe content of ZrO₂ exceeds 6%, devitrification readily occurs duringmelting, and the quality of the chemically strengthened glass may bedeteriorated. The content of ZrO₂ is preferably 6% or less, morepreferably 5% or less, and still more preferably 4% or less.

In the crystallized glass containing lithium metasilicate, for theprecipitation of a lithium metasilicate crystal, the ZrO₂ content ispreferably 1% or more, more preferably 2% or more, still more preferably4% or more, particularly preferably 6% or more, and most preferably 7%or more. However, for suppressing devitrification during melting, thecontent of ZrO₂ is preferably 15% or less, more preferably 14% or less,still more preferably 12% or less, and particularly preferably 11% orless.

In the case of precipitating a β-spodumene crystal and containing bothSnO₂ and ZrO₂, in order to enhance the transparency, the ratioSnO₂/(SnO₂+ZrO₂) of the SnO₂ amount to the total amount of the both ispreferably 0.3 or more, more preferably 0.35 or more, and still morepreferably 0.45 or more.

On the other hand, in order to increase the strength, theSnO₂/(SnO₂+ZrO₂) is preferably 0.7 or less, more preferably 0.65 orless, and still more preferably 0.60 or less.

TiO₂ serves as a component forming a crystal nucleus of the crystallizedglass and therefore may be contained. In the case of precipitating aβ-spodumene crystal and containing TiO₂, the content thereof ispreferably 0.1% or more, more preferably 0.15% or more, and still morepreferably 0.2% or more. On the other hand, if the content of TiO₂exceeds 5%, devitrification readily occurs during melting, and thequality of the chemically strengthened glass may be deteriorated.Therefore, the content is preferably 5% or less, more preferably 3% orless, and still more preferably 1.5% or less.

In the case of precipitating a lithium metasilicate crystal andcontaining TiO₂, the content thereof is preferably 0.5% or more, morepreferably 0.1% or more, still more preferably 2% or more, particularlypreferably 3% or more, and most preferably 4% or more. On the otherhand, if the content of TiO₂ exceeds 10%, devitrification readily occursduring melting, and the quality of the chemically strengthened glass maybe deteriorated. Therefore, the content is preferably 10% or less, morepreferably 8% or less, and still more preferably 6% or less.

In the case where Fe₂O₃ is contained in glass and the glass containsTiO₂, a composite called an ilmenite composite is formed, and yellow orbrown coloring is likely to occur. Fe₂O₃ is normally contained asimpurity in glass and therefore, in order to prevent coloring, thecontent of TiO₂ is preferably 1% or less, more preferably 0.5% or less,still more preferably 0.25% or less, and it is particularly preferablethat the glass is substantially free of TiO₂.

P₂O₅ is not essential but has an effect of encouraging phase separationof the glass and promoting the crystallization and therefore, may becontained. In the case of containing P₂O₅, its content is preferably0.1% or more, more preferably 0.5% or more, still more preferably 1% ormore, and particularly preferably 2% or more. In the case ofprecipitating a lithium metasilicate crystal, the content of P₂O₅ ismore preferably 4% or more, still more preferably 5% or more, andparticularly preferably 6% or more. On the other hand, if the content ofP₂O₅ is large, acid resistance is deteriorated. Accordingly, the contentof P₂O₅ is 15% or less, preferably 14% or less, more preferably 12% orless, still more preferably 11% or less, yet still more preferably 10%or less, particularly preferably 8% or less, and most preferably 7% orless. In the case of a chemically strengthened glass containing aβ-spodumene crystal, in order to make fragments less likely scatter uponbreakage, the content of P₂O₅ is preferably 6% or less, more preferably5% or less, still more preferably 4% or less, particularly preferably 3%or less, and most preferably 2% or less. In the case of placingimportance on the acid resistance, it is preferable to be substantiallyfree of P₂O₅.

B₂O₃ is a component enhancing the chipping resistance and meltability ofthe glass for chemical strengthening or the chemically strengthenedglass and may be contained. Although B₂O₃ is not essential, in the caseof containing B₂O₃, the content thereof is preferably 0.5% or more, morepreferably 1% or more, still more preferably 2% or more, for enhancingthe meltability. On the other hand, if the content of B₂O₃ exceeds 5%,striae are generated during melting and the quality of the glass forchemical strengthening is easily deteriorated. Therefore, the content ofB₂O₃ is preferably 5% or less, more preferably 4% or less, still morepreferably 3% or less, and particularly preferably 1% or less. In orderto increase the acid resistance, it is preferable to be substantiallyfree of B₂O₃.

MgO is a component increasing the surface compressive stress of thechemically strengthened glass, is a component suppressing scattering offragments upon breakage of the chemically strengthened glass, and may becontained. In the case of containing MgO, its content is preferably 0.5%or more, and more preferably 1% or more. On the other hand, in order tosuppress devitrification during melting, the content of MgO ispreferably 5% or less, more preferably 4% or less, and still morepreferably 3% or less.

CaO is a component enhancing the meltability of the glass and may becontained so as to prevent devitrification during melting and enhancethe meltability while suppressing a rise in the thermal expansioncoefficient. In the case of containing CaO, the content thereof ispreferably 0.5% or more, and more preferably 1% or more. On the otherhand, in order to enhance the ion exchange properties, the content ofCaO is preferably 4% or less, more preferably 3% or less, andparticularly preferably 2% or less.

SrO is a component enhancing the meltability of the glass, is also acomponent enhancing the refractive index of the glass to make therefractive index of the residual glass phase after crystallization closeto the refractive index of the precipitated crystal, thereby improvingthe light transmittance of the crystallized glass. Therefore, SrO may becontained. In the case of containing SrO, the content thereof ispreferably 0.1% or more, more preferably 0.5% or more, and still morepreferably 1% or more. On the other hand, if the content of SrO is toolarge, the ion exchange rate decreases. Accordingly, the content of SrOis preferably 3% or less, more preferably 2.5% or less, still morepreferably 2% or less, and particularly preferably 1% or less.

BaO is a component enhancing the meltability of the glass, is also acomponent enhancing the refractive index of the glass to make therefractive index of the residual glass phase after crystallization closeto the refractive index of the lithium aluminosilicate crystal phase,thereby improving the light transmittance of the crystallized glass.Therefore, BaO may be contained. In the case of containing BaO, thecontent thereof is preferably 0.1% or more, more preferably 0.5% ormore, and still more preferably 1% or more. On the other hand, if theBaO content is too large, the ion exchange rate decreases. Accordingly,the content of BaO is preferably 3% or less, more preferably 2.5% orless, still more preferably 2% or less, and particularly preferably 1%or less.

ZnO is a component decreasing the thermal expansion coefficient of theglass and increasing the chemical durability, is also a componentenhancing the refractive index of the glass to make the refractive indexof the residual glass phase after crystallization close to therefractive index of the lithium aluminosilicate crystal phase, therebyimproving the light transmittance of the crystallized glass. Therefore,ZnO may be contained. In the case of containing ZnO, the content thereofis preferably 0.5% or more, more preferably 1% or more, still morepreferably 1.5% or more, and particularly preferably 2% or more. On theother hand, for suppressing devitrification during melting, the contentof ZnO is preferably 4% or less, more preferably 3% or less, and stillmore preferably 2% or less.

All of Y₂O₃, La₂O₃, Nb₂O₅ and Ta₂O₅ are effective in preventingfragments from scattering upon breakage of the glass and may becontained so as to increase the refractive index. In the case ofcontaining these components, the total Y₂O₃+La₂O₃+Nb₂O₅ of the contentsof Y₂O₃, La₂O₃ and Nb₂O₅ is preferably 0.5% or more, more preferably 1%or more, still more preferably 1.5% or more, and particularly preferably2% or more. Furthermore, for the reason that the glass is less likely todevitrify during melting, Y₂O₃+La₂O₃+Nb₂O₅ is preferably 4% or less,more preferably 3% or less, still more preferably 2% or less, andparticularly preferably 1% or less.

The total content Y₂O₃+La₂O₃+Nb₂O₅+Ta₂O₅ of Y₂O₃, La₂O₃, Nb₂O₅ and Ta₂O₅is preferably 0.5% or more, more preferably 1% or more, still morepreferably 1.5% or more, and particularly preferably 2% or more.Furthermore, for the reason that the glass is less likely to devitrifyduring melting, Y₂O₃+La₂O₃±Nb₂O₅+Ta₂O₅ is preferably 4% or less, morepreferably 3% or less, still more preferably 2% or less, andparticularly preferably 1% or less.

In addition, CeO₂ may be contained. CeO₂ is effective in oxidizingglass. In the case of containing a large amount of SnO₂, CeO₂ mayinhibit SnO₂ from being reduced to SnO that is a coloring component,thereby suppressing coloring. In the case of containing CeO₂, thecontent thereof is preferably 0.03% or more, more preferably 0.05% ormore, and still more preferably 0.07% or more. In the case of using CeO₂as an oxidizer, if the content of CeO₂ is too large, the glass isreadily colored. Therefore, for enhancing the transparency, the contentof CeO₂ is preferably 1.5% or less, and more preferably 1.0% or less.

Furthermore, as long as the attainment of desired chemical strengtheningproperties is not impeded, a coloring component may be added. Preferableexamples of coloring components include Co₃O₄, MnO₂, Fe₂O₃, NiO, CuO,Cr₂O₃, V₂O₅, Bi₂O₃, SeO₂, Er₂O₃, and Nd₂O₃.

The content of the coloring components is preferably 1% or less intotal. In the case of increasing the light transmittance of the glass,it is preferable that the glass is substantially free of thesecomponents.

In addition, SO₃, a chloride, a fluoride, etc. may be appropriatelycontained as a refining agent at the time of glass melting. It ispreferable not to contain As₂O₃. In the case of containing Sb₂O₃, thecontent thereof is preferably 0.3% or less, more preferably 0.1% orless, and most preferably nil.

<Production Method of Glass for Chemical Strengthening>

The production method of a glass for chemical strengthening of thisembodiment is a production method of a glass for chemical strengtheningincluding heating and crystallizing an amorphous glass and bend-formingthe resulting present crystallized glass under heating. The presentthree-dimensionally shaped glass can be produced by the productionmethod of a glass for chemical strengthening of the present invention.

In addition, the production method of a chemically strengthened glass ofthis embodiment is a production method of a chemically strengthenedglass including heating and crystallizing an amorphous glass,bend-forming the resulting present crystallized glass under heating, andthereafter chemically strengthening the glass. The three-dimensionallyshaped chemically strengthened glass of this embodiment is obtained bythe production method of a chemically strengthened glass of thisembodiment.

(Production of Amorphous Glass)

The amorphous glass can be produced, for example, by the followingmethod. Note that the following production method is an example ofproducing a sheet-like chemically strengthened glass.

Glass raw materials are prepared to obtain a glass having a desiredcomposition, and heated and melted in a glass melting furnace. Afterthat, the molten glass is homogenized by bubbling, stirring, addition ofa refining agent, etc., then formed into a glass sheet with apredetermined thickness by a known forming method, and annealed.Alternatively, the molten glass may be formed into a sheet by a methodin which the molten glass is formed into a block, annealed, and thencut.

Examples of the forming method of the sheet-like glass include a floatprocess, a press process, a fusion process, and a down draw process.Particularly in the case of producing a large-size glass sheet, a floatprocess is preferred. In addition, a continuously forming method otherthan a float process, for example, a fusion process or a down drawprocess, is also preferred.

(Crystallization Treatment)

A crystallized glass is obtained by heat-treating the amorphous glassobtained by the procedure above.

The heating treatment is preferably a two-step heating treatment inwhich the temperature is raised from room temperature to a firsttreatment temperature, followed by holding for a given time, and thenraised to a second treatment temperature higher than the first treatmenttemperature, followed by holding for a given time. The heating treatmentis also preferably a three-step heating treatment in which thetemperature is raised from room temperature to a first treatmenttemperature, followed by holding for a given time, then raised to asecond treatment temperature higher than the first treatmenttemperature, followed by holding for a given time, and further raised toa third treatment temperature higher than the second treatmenttemperature, followed by holding for a given time.

In the case of the two-step heating treatment, the first treatmenttemperature is preferably within a temperature range at which thecrystal nucleation rate increases in the glass composition, and thesecond treatment temperature is preferably within a temperature range atwhich the crystal growth rate increases in the glass composition. Inaddition, the holding time at the first treatment temperature ispreferably long enough to produce a sufficient number of crystal nuclei.When a large number of crystal nuclei are produced, the size of eachcrystal is reduced and consequently a crystallized glass having hightransparency is obtained.

The first treatment temperature is, for example, from 550 to 800° C.,and the second treatment temperature is, for example, from 850 to 1,000°C. The first treatment temperature is held for 2 to 10 hours, and thesecond treatment temperature is then held for 2 to 10 hours.

The crystallized glass obtained by the procedure above is ground andpolished as necessary, to form a crystallized glass sheet. In the casewhere the crystallized glass sheet is cut into a predetermined shape andsize or chamfered, cutting or chamfering is preferably performed beforeapplying a chemical strengthening treatment, because a compressivestress layer is formed also on the end face by the later chemicalstrengthening treatment.

(Bend-Forming)

As for the bend-forming method, any method can be selected from existingbend-forming methods such as self-weight forming method, vacuum formingmethod and press forming method. Two or more kinds of bend-formingmethods may be used in combination.

The self-weight forming method is a method in which a glass sheet isplaced on a forming mold and the glass sheet is heated, then made to fitthe forming mold by gravity to be bend-formed into a predeterminedshape.

The vacuum forming method is a method in which a glass sheet is placedon a forming mold and after the periphery of the glass sheet is sealed,a space between the forming mold and the glass sheet is depressurized toapply a differential pressure between the front and back surfaces of theglass sheet so as to perform bend-forming. On this occasion, a pressuremay be supplementarily applied to the upper surface side of the glasssheet.

The press forming is a method in which a glass sheet is placed betweenforming molds (upper mold and lower mold) and the glass sheet is heatedand bend-formed into a predetermined shape by applying a press loadbetween the upper and lower molds.

In any case, the glass is deformed by applying a force while the glassis heated.

The bend-forming (thermal bending) temperature is, for example, from 700to 1,100° C., and preferably from 750 to 1,050° C. In view of dimensionaccuracy, the thermal bending temperature is preferably high relative tothe maximum temperature of the crystallization treatment because thermaldeformation readily occurs. The difference between the maximumtemperature of the crystallization treatment and the thermal bendingtemperature is preferably 10° C. or more, and more preferably 30° C. ormore. On the other hand, if the thermal bending temperature is too highrelative to the crystallization treatment temperature, the lighttransmittance may be deteriorated by the bend-forming. Accordingly, thedifference between the maximum temperature of the crystallizationtreatment and the thermal bending temperature is preferably 120° C. orless, more preferably 100° C. or less, still more preferably 90° C. orless, and particularly preferably 60° C. or less.

The decrease of light transmittance by bend-forming is preferably 3% orless, more preferably 2% or less, still more preferably 1.5% or less,and particularly preferably 1% or less.

In addition, for keeping the transparency of the final glass high, ahigher light transmittance before thermal bending is advantageous, andthe light transmittance in terms of a thickness of 0.8 mm is preferably85% or more, more preferably 87% or more, and particularly preferably89% or more.

(Chemical Strengthening Treatment)

The chemical strengthening treatment is a treatment in which a glass isbrought into contact with a metal salt by a method of, for example,immersing the glass in a metal salt (e.g., potassium nitrate) meltcontaining a metal ion having a large ionic radius (typically, Na ion orK ion), and a metal ion having a small ionic radius (typically Na ion orLi ion) in the glass is thereby replaced by a metal ion having a largeionic radius (typically Na ion or K ion for Li ion, and K ion for Naion).

In order to increase the rate of the chemical strengthening treatment,it is preferable to use “Li—Na exchange” of replacing Li ion in theglass by Na ion. Furthermore, in order to form a large compressivestress by ion exchange, it is preferable to use “Na—K exchange” ofreplacing Na ion in the glass by K ion.

Examples of the molten salt for performing the chemical strengtheningtreatment include a nitrate, a sulfate, a carbonate, and a chloride.Among these, examples of the nitrate include lithium nitrate, sodiumnitrate, potassium nitrate, cesium nitrate, and silver nitrate. Examplesof the sulfates include lithium sulfate, sodium sulfate, potassiumsulfate, cesium sulfate, and silver sulfate. Examples of the carbonateinclude lithium carbonate, sodium carbonate, and potassium carbonate.Examples of the chloride include lithium chloride, sodium chloride,potassium chloride, cesium chloride, and silver chloride. One of thesemolten salts may be used alone, or a plurality of kinds thereof may beused in combination.

The treatment conditions such as time and temperature of the chemicalstrengthening treatment may be appropriately selected while taking intoaccount the glass composition, the kind of molten salt, etc.

The present strengthened glass is preferably obtained, for example, bythe following two-step chemical strengthening treatment.

First, the present three-dimensionally shaped glass is immersed in an Naion-containing metal salt (e.g., sodium nitrate) at approximately from350 to 500° C. for approximately from 0.1 to 10 hours. This causes ionexchange between Li ion in the present three-dimensionally shaped glassand Na ion in the metal salt, and for example a compressive stress layerhaving a surface compressive stress of 200 MPa or more and a depth ofcompressive stress layer of 80 μm or more can thereby be formed. If thesurface compressive stress introduced by this treatment exceeds 1,000MPa, it is difficult to increase DOL while keeping CT low in the finallyobtained present strengthened glass. Accordingly, the surfacecompressive stress introduced by this treatment is preferably 900 MPa orless, more preferably 700 MPa or less, and still more preferably 600 MPaor less.

Next, the glass after the treatment above is immersed in a Kion-containing metal salt (e.g., potassium nitrate) at approximatelyfrom 350 to 500° C. for approximately from 0.1 to 10 hours. A largecompressive stress is consequently generated, for example, in a portionat a depth of about 10 μm or less of the compressive stress layer formedin the previous treatment.

According to such a two-step treatment, a favorable stress profile witha surface compressive stress of 600 MPa or more is likely to beobtained.

The glass may be immersed in the K ion-containing metal salt after theglass is first immersed in the Na ion-containing metal salt and thenheld at 350 to 500° C. in the atmosphere for 1 to 5 hours. The holdingtemperature is preferably from 425 to 475° C., and more preferably from440 to 460° C.

Holding at a high temperature in the atmosphere allows Na ionsintroduced inside the glass from the metal salt by the first treatmentto thermally diffuse in the glass, leading to formation of a morefavorable stress profile.

Alternatively, instead of holding in the atmosphere after immersion inan Na ion-containing metal salt, the glass may be immersed in a metalsalt containing Na ion and Li ion (for example, a mixed salt of sodiumnitrate and lithium nitrate) at 350 to 500° C. for 0.1 to 20 hours.

Immersion in the metal salt containing Na ion and Li ion causes ionexchange between Na ion in the glass and Li ion in the metal salt toform a more favorable stress profile, thereby improving the dropstrength to asphalt.

In the case of performing such a two-step or three-step strengtheningtreatment, in view of production efficiency, the total treatment time ispreferably 10 hours or less, more preferably 5 hours or less, and stillmore preferably 3 hours or less. On the other hand, in order to obtain adesired stress profile, the total treatment time needs to be 0.5 hoursor more, and more preferably 1 hour or more.

The three-dimensionally shaped chemically strengthened glass of thepresent embodiment obtained in the above-described manner is usefulparticularly as a cover glass used, for example, in a mobile device suchas cell phone and smartphone. The glass is also useful for a cover glassof a display device not intended to be portable, such as television,personal computer and touch panel. The glass is also useful as a coverglass of, for example, an interior decoration of a car, an airplane,etc.

EXAMPLE

The present invention is described below by referring to Examples, butthe present invention is not limited thereto.

Glass raw materials of each of Glasses 1 to 8 were prepared to give aglass composition shown by mass % on an oxide basis in Table 1, andweighed so that 800 g of a glass can be obtained. Subsequently, themixed glass raw materials were put in a platinum crucible, charged intoan electric furnace at 1,500 to 1,700° C., melted for about 5 hours,degassed, and homogenized.

The obtained molten glass was cast into a mold, held for 1 hour at atemperature 30° C. higher than the glass transition point, and thencooled down to room temperature at a rate of 0.5° C./min to obtain aglass block.

(Glass Transition Point)

Based on JIS R1618:2002, a thermal expansion curve was obtained using athermal dilatometer (TD5000SA made by Bruker AXS GmbH.) by setting thetemperature riserate to 10° C./min. In addition, a glass transitionpoint Tg [unit: ° C.] was determined from the obtained thermal expansioncurve. The results are shown in Table 1. In the Table, the blankindicates unevaluated.

TABLE 1 Glass 1 Glass 2 Glass 3 Glass 4 Glass 5 Glass 6 Glass 7 Glass 8SiO₂ 65.4 62.9 66.1 73.6 59.5 57.7 53.8 51.2 Al₂O₃ 22.4 22.4 21.0 7.62.0 2.0 7.2 8.7 Li₂O 4.3 4.3 1.9 11.2 18.4 18.5 18.1 17.4 Na₂O 2.0 2.00.5 1.6 2.0 5.6 4.4 1.9 K₂O 0.0 0.0 0.0 0.0 2.0 0.0 0.8 1.9 ZrO₂ 2.3 2.34.8 3.7 10.1 10.1 9.9 9.5 SnO₂ 2.1 2.1 0.0 0.0 0.0 0.0 0.0 0.0 P₂O₅ 1.53.0 0.0 2.1 5.9 6.0 5.8 5.6 B₂O₃ 0.0 0.0 0.0 0.2 0.0 0.0 0.0 0.0 Y₂O₃0.0 0.0 0.0 0.0 0.0 0.0 0.0 3.9 SrO 0.0 1.0 0.0 0.0 0.0 0.0 0.0 0.0 MgO0.0 0.0 5.7 0.0 0.0 0.0 0.0 0.0 Tg 739 714 453 440 460 471

Ex. 1 to Ex. 14 and Ex. 16 to Ex. 19

The obtained glass block was processed into a sheet of approximately 60mm×60 mm×1.5 mm and heat-treated under the conditions shown in Table 2or 3 to obtain a crystallized glass (Ex. 1 to Ex. 14, and Ex. 16 to Ex.19). In the column of crystallization treatment of Tables, when two-steptreatment conditions are described, this means that the glass sheet washeld at the temperature and for the time shown in the upper stage andthen held at the temperature and for the time shown in the lower stage.For example, when 750° C. 4 h is written in the upper stage and 920° C.4 h is written in the lower stage, this means that the glass sheet washeld at 750° C. for 4 hours and then held at 920° C. for 4 hours. Inaddition, when three-step treatment conditions are described, this meansthat the glass sheet was held at the temperature and for the time shownin the upper stage, then held at the temperature and for the time shownin the middle stage, and furthermore held at the temperature and for thetime shown in the lower stage.

The obtained crystallized glass was evaluated for the density, Young'smodulus, thermal expansion coefficient, precipitated crystal, Vickershardness, fracture toughness value, light transmittance, and bendformability as follows. In addition, chemical strengthening treatmentwas performed and the strengthening properties were evaluated. Theresults are shown in Table 2 or 3. The blank in the Table indicatesunmeasured.

(Density)

The density [unit: g/cm³] was measured by the Archimedes method afterprocessing by minor polishing into a thickness of 0.8 mm.

(Young's Modulus)

The Young's modulus [unit: GPa] was measured by an ultrasonic methodafter processing by mirror polishing into a thickness of 0.8 mm.

(Thermal Expansion Coefficient)

A thermal expansion curve was obtained using a thermal dilatometer(TD5000SA manufactured by Bruker AXS GmbH.) by setting the temperaturerise rate at 10° C./min. In addition, an average linear thermalexpansion coefficient [unit: ×10⁻⁷/° C.] at 50° C. to 350° C. wasmeasured from the obtained thermal expansion curve.

(Precipitated Crystal)

Powder X-ray diffraction was measured under the following conditions toidentify the precipitated crystal (main crystal). In addition,crystallinity (degree of crystallinity) [unit: %] and crystal grain size(crystal size) [unit: nm] were calculated using a Rietveld method. Inthe Tables, βSP stands for a β-spodumene crystal, P stands for apetalite crystal, LD stands for lithium disilicate, LS stands forlithium metasilicate, and βQ stands for β-quartz.

Measurement apparatus: SmartLab manufactured by Rigaku Corporation

X-Ray: CuKα radiation

Measurement Range: 20=from 10° to 80°

Speed: 10°/min

Step: 0.02°

(Light Transmittance)

After processing by mirror polishing into a thickness of 0.8 mm, anaverage transmittance (transmittance before forming, transmittance afterforming) [unit: %] for light at a wavelength of 380 to 780 nm wasmeasured before the later-described bend formability test and after thetest with a configuration using, as a detector, an integrating sphereunit for a spectrophotometer (LAMBDA950 manufactured by PerkinElmer,Inc.), and the difference therebetween was also calculated.

(Vickers Hardness)

The Vickers hardness was measured by pressing an indenter under a loadof 100 gf for 15 seconds by use of a Shimadzu micro-Vickers hardnesstester (HMV-2 manufactured by Shimadzu Corporation). Incidentally, theVickers hardness was measured in the same manner also after thelater-described chemical strengthening treatment (Vickers hardnessbefore strengthening, Vickers hardness after strengthening).

(Fracture Toughness Value)

Based on JIS R1607:2010, a fracture toughness value after a chemicalstrengthening treatment (fracture toughness value after strengthening)was determined by an indentation fracture method (IF method) using aVickers hardness tester (FLC-50V manufactured by Future-Tech Corp.).Indentation was performed under a load of 3 kgf in an atmosphere at atemperature of 22° C. and a relative humidity of 40%. The indentationlength was measured in the same atmosphere 20 minutes after theindentation. Measurement was performed at 10 points for each sample, andan average value was calculated and taken as the fracture toughnessvalue [unit: MPa·m^(1/2)].

(Bend Formability)

A high alumina insulating firebrick (BAL-99 manufactured by IsoliteInsulating Products Co., Ltd.) was processed to prepare two supportingbricks 1 and one loading brick 3, each having a rod shape of 20 mm×20mm×120 mm. Supporting bricks 1 were placed in parallel at an interval of40 mm in an electric furnace, and the loading brick 3 was also placed inthe same electric furnace, followed by preheating.

The obtained crystallized glass was processed into 60 mm×10 mm×0.8 mm,and both surfaces of 60 mm×10 mm were mirror-polished. In an electricfurnace kept at a bending temperature shown in Table 2 or 3, asillustrated in (a) of FIG. 6, the crystallized glass sheet 2 was put ontwo supporting bricks 1, the loading brick 3 (weight: 85 g) was put onthe crystallized glass sheet 2, and these were held for 10 minutes.After the elapse of 10 minutes, the loading brick 3 was removed from thesurface of the crystallized glass sheet 2, and the crystallized glasssheet 2 was taken out from the electric furnace and cooled. Thereafter,the deformation amount h (bend-deformation amount) of the crystallizedglass, as illustrated in (b) of FIG. 6, was measured. In Tables, “-”means that the glass was scarcely deformed and the deformation amountcould not be measured.

(Bend Formability 2)

With respect to Ex. 16 to Ex. 19, a bend-forming test described belowwas separately performed.

First, carbon-made concave mold and convex mold which were designed forforming a curved surface having a curvature radius of 6.0 mm, a bendingangle of 70.5° and a bending depth of 4.0 mm were prepared. And then thecrystallized glass sheet was placed near the center of the glass contactsurface of the concave mold.

Subsequently, preheating, deformation and cooling were performed using aforming device. Incidentally, the preheating was performed at atemperature at which the crystallized glass has an equilibrium viscosityof about 10¹⁸ Pa·s. The deformation was performed by moving the convexmold downward at a temperature at which the crystallized glass has anequilibrium viscosity of about 10^(11.5) Pa·s, followed by pressing theglass with 2,000 N at a maximum.

By the treatment above, the crystallized glasses of all of Ex. 16 to Ex.19 were formed into a three-dimensional shape having a curvature radiusof 2,000 mm.

The above-described test indicated that the crystallized glasses of Ex.16 to Ex. 19 can be formed into a desired shape.

<Chemical Strengthening Treatment>

The obtained crystallized glass was subjected to a chemicalstrengthening treatment under the following conditions.

In Ex. 1 to Ex. 8, the glass was immersed in a molten salt of sodiumnitrate at 450° C. for 30 minutes, then immersed in a molten salt ofpotassium nitrate at 450° C. for 30 minutes, thereby performing chemicalstrengthening.

In Ex. 9 to Ex. 11, the glass was immersed in a lithiumsulfate-potassium sulfate mixed salt (in which the mass ratio betweenthe lithium sulfate and potassium sulfate was 90:10) at 740° C. for 240minutes, thereby performing chemical strengthening.

In Ex. 12 to Ex. 14, the glass was immersed in sodium nitrate at 430° C.for 2 hours, then immersed in potassium nitrate at 430° C. for 2 hours,thereby performing chemical strengthening.

In Ex. 16 to Ex. 19, the glass was immersed in sodium nitrate at 450° C.for 3 hours, then immersed in potassium nitrate at 450° C. for 1 hour,thereby performing chemical strengthening.

(Chemical Strengthening Properties)

A stress value was measured using a surface stress meter FSM-6000manufactured by Orihara Manufacturing Co., Ltd. and a measuring deviceSLP1000 utilizing scattered-light photoelasticity manufactured byOrihara Manufacturing Co., Ltd., and a compressive stress value CS[unit: MPa] on the glass surface, a depth DOL [unit: μm] at which thecompressive stress value becomes zero, an internal tensile stress (CT)[unit: MPa], and a maximum depth (50 MPa depth) [unit: μm] at which thecompressive stress value is 50 MPa or more, were read out. In addition,m₁ represented by the following expression was determined from the depthDOL₁ at which the compressive stress value is CS/2.

m ₁=(CS−CS/2)/(0−DOL ₁)

m₂ represented by the following expression was determined from thecompressive stress CS₁ at the depth DOL/4 and the compressive stress CS₂at the depth DOL/2.

m ₂=(CS ₁ −CS ₂)/(DOL/4−DOL/2)

m₃ represented by the following expression was determined from thecompressive stress CS₂ at the depth DOL/2.

m ₃=(CS ₂−0)/(DOL/2−DOL)

These results are shown in Table 2 or 3. In the Table, the blankindicates unmeasured.

TABLE 2 Ex. 1 Ex . 2 Ex. 3 Ex. 4 Ex. 5 Glass Glass 1 Glass 1 Glass 1Glass 1 Glass 1 Crystallization 750° C. 750° C. 750° C. 750° C. 750° C.treatment 4 h 4 h 4 h 4 h 4 h 920° C. 920° C. 920° C. 900° C. 880° C. 4h 4 h 4 h 4 h 4 h Density 2.492 2.492 2.492 Young's modulus 88 88 88Thermal expansion 12 12 12 coefficient Main crystal βSP βSP βSP βSP βSPDegree of crystallinity 25 25 25 Crystal size 55 55 55 Transmittancebefore 87.3 87.3 87.3 87.3 88.2 forming Bending temperature 1000° C.900° C. 1100° C. 1000° C. 1000° C. Transmittance after 85.7 86.5 76.885.0 83.1 forming Difference in 1.6 0.8 10.5 2.3 5.1 transmittancebefore and after forming Bend-deformation amount 1.2 mm — more than 10mm 1.5 mm — Vickers hardness before 780 780 780 strengthening Vickershardness after 830 830 830 strengthening Fracture toughness value 1.21.2 1.2 after strengthening CS 1135 1135 1135 DOL 110 110 110 CT 65 6565 m₁ −104 −104 −104 m₂ −4.0 −4.0 −4.0 m₃ −3.0 −3.0 −3.0 50 MPa Depth 9595 95 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Glass Glass 2 Glass 2 Glass 2 Glass3 Glass 3 Crystallization 750° C. 750° C. 750° C. 750° C. 750° C.treatment 4 h 4 h 4 h 4 h 4 h 900° C. 900° C. 900° C. 920° C. 920° C. 4h 4 h 4 h 4 h 4 h Density 2.48 2.48 2.48 2.9 Young's modulus 86 86 86 9898 Thermal expansion 12 12 12 coefficient Main crystal βSP βSP βSP βQ βQDegree of crystallinity 73 73 73 Crystal size 120 120 120 Transmittance89.4 89.4 89.4 83.0 83.0 before forming Bending temperature 950° C.1000° C. 1100° C. 1000° C. 900° C. Transmittance 88.6 86.8 72.3 80.079.6 after forming Difference in 0.8 2.6 17.1 3 3.4 transmittance beforeand after forming Bend-deformation amount 1.1 mm 10 mm 15 mm 1.5 mm —Vickers hardness before 730 730 730 strengthening Vickers hardness after820 820 820 1040 strengthening Fracture toughness value 1.2 1.2 1.2 1after strengthening CS 1200 1200 1200 590 DOL 120 120 120 50 CT m₁ −104−104 −104 m₂ −4.0 −4.0 −4.0 m₃ −3.0 −3.0 −3.0 50 MPa Depth 95 95 95

TABLE 3 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 16 Ex. 17 Ex. 18 Ex. 19 GlassGlass 3 Glass 4 Glass 4 Glass 4 Glass 5 Glass 6 Glass 7 Glass 8Crystallization 750° C. 540° C. 540° C. 540° C. 550° C. 550° C. 550° C.550° C. treatment 4 h 4 h 4 h 4 h 2 h 2 h 2 h 2 h 920° C. 600° C. 600°C. 600° C. 700° C. 710° C. 710° C. 730° C. 4 h 4 h 4 h 4 h 2 h 2 h 2 h 2h 710° C. 710° C. 710° C. 4 h 4 h 4 h Density 2.59 2.61 2.66 Young'smodulus 98 105 105 105 104 106 105 Thermal expansion 134 131 131 123coefficient Main crystal βQ P, L D P, LD P, LD LS LS LS LS Degree ofcrystallinity 23 Crystal size 20 Transmittance 83.0 91.0 91.0 91.0 90.190.6 90.4 before forming Bending temperature 1100° C. 800° C. 750° C.900° C. 710° C. Transmittance 71.1 89.9 90.9 29.1 90.0 after formingDifference in 11.9 2.1 0.1 61.9 0.1 transmittance before and afterforming Bend-deformation amount more than 10 mm 5 mm — more than 10 mm 5mm Vickers hardness 604 before strengthening Vickers hardness after 730801 823 strengthening Fracture toughness value 0.8 after strengtheningCS 500 630 750 900 760 DOL 130 140 126 CT m₁ m₂ m₃ 50 MPa Depth

Ex. 15

A glass sheet composed of Glass 1 was bent at 1,000° C. in the samemanner as in Ex. 1 and then crystallized under the same crystallizationconditions as in Ex. 1. As a result, deformation was again caused, andthe glass sheet retuned to the same flat sheet shape as the tray usedfor the crystallization treatment. This result indicates that the methodof performing bend-forming after crystallization makes it easy to retaina desired shape.

Ex. 1 to Ex. 3 were crystallized glasses obtained by crystallizing glasssheets composed of Glass 1 under the same crystallization conditions, inwhich a β-spodumene crystal was the main crystal.

In Ex. 1, sufficiently high CS and DOL were obtained after chemicalstrengthening.

In Ex. 2, since the bending temperature was not sufficiently high, thebend-deformation amount was reduced.

In Ex. 3, since the bending temperature was too high, the transparencywas reduced.

It is therefore understood that in the case of producing thecrystallized glass of to the present invention, the bend-formingtemperature must be appropriately adjusted.

Ex. 4 and Ex. 5 were the same as Ex. 1 except that the second treatmenttemperature in the two-step heating treatment (crystallizationtreatment) is low, and the change in transparency due to bendingtreatment was increased, compared with Ex. 1. It is thought that sincecrystallization before bending treatment was insufficient, the change intransmittance at the time of bending treatment was increased.

Ex. 6 to Ex. 8 were crystallized glasses obtained by crystallizing glasssheets composed of Glass 2 under the same crystallization conditions, inwhich a β-spodumene crystal was the main crystal.

In Ex. 6, not only sufficiently high CS and DOL were obtained afterchemical strengthening but also the transmittance before thermal bendingwas as high as 89% or more. Consequently, when thermal bending wasperformed by reducing the difference between the maximum temperature ofthe crystallization treatment and the thermal bending temperature, ahigh transmittance of 88% or more was finally achieved. In addition, asufficiently large bend-deformation amount was obtained.

In Ex. 7, the transmittance before thermal bending was similarly as highas 89% or more. Therefore even when a large bend-deformation amount wasobtained by increasing the difference between the maximum temperature ofthe crystallization treatment and the thermal bending temperature, ahigh transmittance of 86% or more was finally achieved.

In Ex. 8, since the bending temperature was too high, the transmittancewas reduced.

Ex. 9 to Ex. 11 were crystallized glasses obtained by crystallizingglass sheets composed of Glass 3 under the same crystallizationconditions, in which β-quartz was the main crystal.

When Ex. 9 is compared with Ex. 1 and Ex. 6, the change in transmittancedue to the bend-forming treatment was slightly large in Ex. 9.

Ex. 12 to Ex. 14 were crystallized glasses obtained by crystallizingglass sheets composed of Glass 4 under the same crystallizationconditions, and were crystallized glasses containing a petalite crystal.

When Ex. 12 is compared with Ex. 13 and Ex. 14, since the bendingtemperature was not sufficiently high in Ex. 13, the bend-deformationamount was reduced.

In Ex. 14, since the bending temperature was too high, the transparencywas reduced.

It is therefore understood that in the case of processing thecrystallized glass, the bend-forming temperature must be appropriatelyadjusted.

In Ex. 12, since the bending temperature was appropriate, a sufficientlylarge deformation amount was obtained by bend-forming aftercrystallization and moreover the change in transparency was small.

When Ex. 12 is compared with Ex. 1 and Ex. 6, the amount of change bybend forming was large in Ex. 12 which was a crystallized glasscontaining a petalite crystal, and bending thereof was easy.

However, since the compressive stress value (CS) was low and Kc afterstrengthening was small in Ex. 12, Ex. 1 and Ex. 6 which werecrystallized glasses containing a β-spodumene crystal were superior inview of strength.

Ex. 16 to Ex. 19 were crystallized glasses obtained by crystallizingglass sheets composed of Glass 5 to Glass 8, respectively, and all werecrystallized glasses containing a lithium metasilicate crystal.

A crystallized glass containing a lithium metasilicate crystal ischaracterized in that not only sufficiently high CS and DOL are obtainedafter chemical strengthening but also the transmittance before thermalbending is high. It is seen that when forming is performed at anappropriate bending temperature as in Ex. 16, a sufficiently largedeformation amount is obtained and at the same time, the change intransparency can be suppressed.

While the present invention has been described in detail and withreference to specific embodiments thereof, it is apparent to one skilledin the art that various changes and modifications can be made thereinwithout departing from the spirit and scope of the present invention.The present application is based on a Japanese patent application filedon Feb. 27, 2018 (Japanese Patent Application No. 2018-33693) and aJapanese patent application filed on Feb. 8, 2019 (Japanese PatentApplication No. 2019-21896), the entireties of which are incorporated byreference. In addition, all the references cited herein are incorporatedas a whole.

REFERENCE SIGNS LIST

-   1 Supporting brick-   2 Crystallized glass sheet-   3 Loading brick

1. A three-dimensionally shaped crystallized glass comprising a crystal,the glass having a light transmittance of 80% or more in terms of athickness of 0.8 mm and comprising, in mass % on an oxide basis: from 45to 74% of SiO₂; from 1 to 30% of Al₂O₃; from 1 to 25% of Li₂O; from 0 to10% of Na₂O; from 0 to 5% of K₂O; from 0 to 15% in total of either oneor more of SnO₂ and ZrO₂; and from 0 to 12% of P₂O₅.
 2. Thethree-dimensionally shaped crystallized glass according to claim 1,comprising, in mass % on an oxide basis: from 58 to 74% of SiO₂; from 5to 30% of Al₂O₃; from 1 to 14% of Li₂O; from 0 to 5% of Na₂O; from 0 to2% of K₂O; from 0.5 to 12% in total of either one or more of SnO₂ andZrO₂; and from 0 to 6% of P₂O₅.
 3. The three-dimensionally shapedcrystallized glass according to claim 2, comprising, in mass % on anoxide basis: from 58 to 70% of SiO₂; from 15 to 30% of Al₂O₃; from 2 to10% of Li₂O; from 0 to 5% of Na₂O; from 0 to 2% of K₂O; from 0.5 to 6%of SnO₂; from 0.5 to 6% of ZrO₂; and from 0 to 6% of P₂O₅, in whichNa₂O+K₂O is from 1 to 5%.
 4. The three-dimensionally shaped crystallizedglass according to claim 1, comprising, in mass % on an oxide basis:from 45 to 70% of SiO₂; from 1 to 20% of Al₂O₃; from 10 to 25% of Li₂O;from 0 to 10% of Na₂O; from 0 to 5% of K₂O; from 0 to 15% of ZrO₂; andfrom 0 to 12% of P₂O₅.
 5. The three-dimensionally shaped crystallizedglass according to claim 1, comprising a β-spodumene crystal.
 6. Thethree-dimensionally shaped crystallized glass according to claim 1,comprising a petalite crystal.
 7. The three-dimensionally shapedcrystallized glass according to claim 1, comprising a lithiummetasilicate crystal.
 8. The three-dimensionally shaped crystallizedglass according to claim 1, having a Vickers hardness of 780 or more. 9.A three-dimensionally shaped chemically strengthened glass having acompressive stress layer on a surface thereof, the glass being acrystallized glass comprising a crystal, having a light transmittance of80% or more in terms of a thickness of 0.8 mm and comprising, in mass %on an oxide basis: from 45 to 74% of SiO₂; from 1 to 30% of Al₂O₃; from1 to 25% of Li₂O; from 0 to 10% of Na₂O; from 0 to 5% of K₂O; from 0 to15% in total of either one or more of SnO₂ and ZrO₂; and from 0 to 12%of P₂O₅.
 10. The three-dimensionally shaped chemically strengthenedglass according to claim 9, comprising, in mass % on an oxide basis:from 58 to 74% of SiO₂; from 5 to 30% of Al₂O₃; from 1 to 14% of Li₂O;from 0 to 5% of Na₂O; from 0 to 2% of K₂O; from 0.5 to 12% in total ofeither one or more of SnO₂ and ZrO₂; and from 0 to 6% of P₂O₅.
 11. Thethree-dimensionally shaped chemically strengthened glass according toclaim 9, comprising, in mass % on an oxide basis: from 45 to 70% ofSiO₂; from 1 to 20% of Al₂O₃; from 10 to 25% of Li₂O; from 0 to 10% ofNa₂O; from 0 to 5% of K₂O; from 0 to 15% of ZrO₂; and from 0 to 12% ofP₂O₅.
 12. The three-dimensionally shaped chemically strengthened glassaccording to claim 9, comprising a β-spodumene crystal.
 13. Thethree-dimensionally shaped chemically strengthened glass according toclaim 9, comprising a lithium metasilicate crystal.
 14. Thethree-dimensionally shaped chemically strengthened glass according toclaim 9, having a Vickers hardness of 800 or more.
 15. Thethree-dimensionally shaped chemically strengthened glass according toclaim 9, having a surface compressive stress of 600 MPa or more and adepth of the compressive stress layer of 80 μm or more.
 16. A productionmethod of a glass for chemical strengthening, the method comprising:heating and crystallizing a glass comprising, in mass % on an oxidebasis: from 45 to 74% of SiO₂; from 1 to 30% of Al₂O₃; from 1 to 25% ofLi₂O; from 0 to 10% of Na₂O; from 0 to 5% of K₂O; from 0 to 15% in totalof either one or more of SnO₂ and ZrO₂; and from 0 to 12% of P₂O₅; andbend-forming a resulting crystallized glass under heating.
 17. Theproduction method of a glass for chemical strengthening according toclaim 16, wherein the glass comprises, in mass % on an oxide basis: from58 to 74% of SiO₂; from 5 to 30% of Al₂O₃; from 1 to 14% of Li₂O; from 0to 5% of Na₂O; from 0 to 2% of K₂O; from 0.5 to 12% in total of eitherone or more of SnO₂ and ZrO₂; and from 0 to 6% of P₂O₅, in whichNa₂O+K₂O is from 1 to 5%.
 18. The production method of a glass forchemical strengthening according to claim 16, wherein the glasscomprises, in mass % on an oxide basis: from 45 to 70% of SiO₂; from 1to 20% of Al₂O₃; from 10 to 25% of Li₂O; from 0 to 10% of Na₂O; from 0to 5% of K₂O; from 0 to 15% of ZrO₂; and from 0 to 12% of P₂O₅.
 19. Aproduction method of a chemically strengthened glass, the methodcomprising chemically strengthening a glass for chemical strengtheningobtained by the method according to claim 16.